<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
 <title>Document</title>
 <style>
    #box{
    border: 50px solid red;
    border-top: 50px solid rgb(21, 0, 255);
   border-left: 50px solid rgb(0, 255, 47);
    border-bottom: 50px solid rgb(255, 208, 0);
    width: 100px; 
   height: 100px;
   }
   </style>
</head>
<body>
<div id="box">这里是第一个盒子</div>
</body>
</html>